iMac Intel 21.5" and 27" (Late 2009-Mid 2010) SSD Upgrade Bundle - iFixit Store
OWC SSD Upgrade Kits for 21.5-Inch iMac (2013 - 2019)
128GB FUSION DRIVE PCIe SSD Apple iMac 21.5" A1418,27" A1419 Late 2013,2014, 2015 | eBay
A-Tech 32GB Kit (4x8GB) RAM for Apple iMac (Late 2012, Late 2013, Late 2014, Mid 2015) | DDR3 1600MHz SODIMM PC3-12800 204-Pin SO-DIMM Max Memory Upgrade at Amazon.com
Apple iMac 21.5” SSD Upgrade (2013-2015) HDD To Solid State Drive (SATA) | Step By Step - YouTube
iMac 27" Late 2015 A1419 4K - SLOW Fusion hard drive replacement with new internal SSD, MUCH FASTER! - YouTube
Amazon.com: 256GB SSD Hard Drive for Apple MacBook Pro Air 11" 13" 15" A1502 A1398 A1465 A1466 (Late 2013-2015) / OSX Sierra/Mac Pro A1481 : Electronics
How-To: Now's the right time to swap your old iMac's hard drive for a fast new SSD - 9to5Mac
Can I upgrade iMac (Late 2015) fusion drive to SSD? | MacRumors Forums